1. Field of the Invention
The invention lies in the field of recovering metals from their ores and other metal containing material by first chlorinating the metals followed by final recovery of the metals from their chlorides.
2. Description of the Prior Art
Competition, the increasing necessity of using lower and lower grade ores, the requirement that metal recovery processes be essentially non-polluting, and other factors have created a demand for a reduction of the costs for recovering metals from their ores and other materials for the pollution-free processes. Conservation and re-use of reagents appears to be the most feasible area for reduction of costs.
U.S. Pat. No. 1,736,659, Mitchell, discloses a process for the recovery of metals from their sulfide ores in which the metals are first chlorinated and then selectively separated. In this process iron is separated from the desired zinc chloride by precipitation of the iron before the zinc recovery step. The disadvantage of this procedure is that substantial zinc losses will occur in the voluminous iron hydroxide precipitate. Further, Mitchell precipitates the zinc product from the original dissolution solution after various attempts at removing impurities from it. Such a system inevitably results in an impure zinc product. The present invention uses a zinc selective extractant by which the zinc is effectively cleanly separated from the dissolving solution without the necessity of prior precipitation of all other impurities. The present process thereby permits a higher recovery of higher purity zinc.
In the Mitchell process an electrolytic cell is used to generate from sodium chloride formed in the zinc precipitation step the base required to precipitate zinc. In the present process the electrolytic cell is used not only for this purpose but primarily to regenerate the sodium chloride stripping agent used to remove the zinc from the extractant so that additional reagent need not be added for stripping. Using sodium chloride regenerated in the process as the stripping agent and including the electrolytic cell in the stripping circuit to remove excess chlorine ions picked up by the stripping solution in stripping obviates the necessity for an additional stripping reagent and an external procedure for removing excess chlorine ions.